I prefer a simple symbol for simple atheism. I like the 'zero' or 'negative' symbol for this reason. I also like the less simple 'Atomic A' symbol in the OP which somehow seems less serious, but adds the hint of scientific scepticism.

There is a guy in Ireland that travels around to televised football games with a John 3:7 banner and John 3:16 on the flip side. He stands behind the goalposts and has been for over 20 years. I used to think it funny but really he is just another deluded Xian. More here is you are bothered.